The development of novel high-performance devices that exploit especially advantageous capabilities had with infrared light and ultraviolet light is ongoing. For instance, advantage is taken of infrared sensing capabilities in practical applications including, to name examples: surface thermometers for non-contact measurement of the surface temperature of an object; resource-probing systems for sensing terrestrial resource distribution from the upper atmosphere; devices for dark-field detection of objects; sensors for detecting human presence, and security systems employing such sensors; and gas-analyzing equipment. Along with the practical realization of these sorts of high-performance infrared-light and ultraviolet-light exploiting devices have been increasing demands for advanced working capabilities from, and cost reductions in, the optically functioning components—for example, various optical components such as window elements and lens elements—incorporated into such devices.
In a conventional method of manufacturing the window elements and lens elements, raw-material powders are mixed together and molded into a predetermined form, then sintered into a sintered body that is furthermore finished to work it into intended form.
The finishing work is carried out by means of grinding and polishing machining processes, but because the work is usually done by milling off ceramic sinters, the finishing-process costs have proven to be very high. In particular, cases in which shapes such as those of aspherical lenses are produced require ultra-precision turning on ultra-precision lathes, and thus have meant high processing costs. At the same time, since the milling is ordinarily off cylindrical workpieces, the cost of disposing of the sinter material is very large, meaning that expenditure for the sinter material that is discarded is also high and as a result that the optical components in their net shape are extremely costly.
In an attempt to reduce such costs, a method of forming an optical element having a density of 99% or more, utilizing a mold employed when molding and sintering, which has been made into net shape, to mold ZnS powder under a vacuum or an inert gas is set out in Japanese Pat. Pub. No. S41-412. Nevertheless, a problem has been that the method requires changing molds, and that productivity is poor, in that with fracturing and chipping being liable to occur when changing molds or handling for transport, because the strength of molded articles in which no binder is used is inferior, yields are poor. Another problem has been that when heating and pressing are performed simultaneously, moreover, impurities within the raw material are prone not to come out, and if raw materials with consequently many impurities are used, products of inferior transmittance are all that will be produced. Lastly, a problem has been that inasmuch trying to rid the articles of impurities means having to prolong the heating time, productivity drops.
An object of the present invention is in respect of infrared-light or ultraviolet-light optical components to eliminate problems like the foregoing and realize a method of inexpensively manufacturing infrared or ultraviolet optical components, such as window elements and lenses, whose infrared- or ultraviolet-light transmittance is favorable. The present invention makes it possible inexpensively to produce, while allowing finishing processes not to be done or at least the expense they consume lessened, ultrafine ceramic optical components of excellent infrared- or ultraviolet-light transmittance.
Materials for infrared optical components and ultraviolet optical components have to date been regarded difficult to alter in form after sintering. The present inventors discovered that by sintering a material in advance until a certain level of pores remain, a propensity to conform to shape alteration, exploiting the pores contained in the sintered body, could be made manifest utilizing a hot press. They also discovered that optimally selecting pore diameter and pore percentage according to the amount by which the form is altered, and optimizing heating temperature, pressing and deforming speed and pressing pressure enables the reshaping of infrared-optical-component and ultraviolet-optical-component materials until net shape to make them into minutely fine sintered bodies, whereby sinters whose infrared- or ultraviolet-light transmittance is excellent and mechanical strength is superior can be produced.